This invention relates to a pressure gauge for measuring the pressure of a tire, more particularly to a pressure gauge with a new construction which can also measure the depth of the grooves in the tread of a tire.
FIG. 1 is a cross sectional view of a pressure gauge according to U.S. Pat. No. 4,715,222. Accordingly, a pressure gauge for measuring the pressure of a tire includes a housing having an indicating board on one side thereof; an axle rotatably mounted in the housing; a pinion member fixedly mounted on the axle; an indicator for displaying the degree of rotation of the axle; a pair of supporting rods fixedly mounted in the housing to support a sheet; a tube member including an inner end extending to the housing and in a perpendicular position relative to the axis of the axle and an outer end extending away from the housing and said outer end being adapted to communicate with the valve of a tire; a seal member movably disposed in the outer end of the tube member, the position of which when engaged with a tire will be determined by the pressure of that tire; an abutting member disposed in and forming a seal with the outer end of the tube member abutting the seal member; a compression spring disposed in the tube member biasing the abutting member and hence the seal member against the pressure exerted on the seal member; a rack member movably disposed in the tube member and having a lower end extending outward from the tube member so as to mesh with the pinion member to rotate the axle; a tension spring connecting the abutting member with the rack member; a post fixedly mounted in the housing for incorporating with the pinion member to restrict the rack member to pass therebetween; a pin pivotedly mounted in the housing as a spring mount; a blocking member normally brought into engagement with the surface of the axle to create friction therebetween when the axle is driven to rotate by the rack member as the abutting member is forced downward by the pressure of a tire, the force of said friction being adjusted higher than the tension force of the tension spring. Only when the blocking member is released from the axle, will the rack member be pulled by the tension spring back to its original position.
In the prior art the pressure gauge can only measure the air pressure of a tire. But cars traveling on long journeys also need good traction and if the grooves on the tread of a tire wear out, that traction is lost and the car can slip or slide on the road. To check the depth of the grooves in the tire tread, the driver needs to carry another device. This situation is inconvenient.